a) Field of the Invention
This invention relates to a safety mechanism for a mechanical trigger device of a gas generator, which generates working gas to actuate a webbing pretensioner for taking up a slack of a webbing so that an occupant can be effectively restrained in a seat upon collision of a vehicle or an air bag system for protecting an occupant by an air bag from an impact upon collision of a vehicle.
To more effectively protect an occupant in the event of an emergency such as a vehicular collision, occupant protecting systems such as webbing pretensioners or air bag systems have found wide-spread utility in recent years.
A webbing pretensioner is provided with a cable wound on a take-up spindle of a webbing retractor. This cable is connected to a piston which is slidably fitted in a cylinder. By displacing the piston within the cylinder under the thrust of an expanding pressure of explosively-expanding working gas, the cable is pulled to rotate the take-up spindle so that any slack of a webbing is taken up to restrain an occupant in a seat.
An air bag system, on the other hand, has an air bag folded and stored, for example, in a center pad of a steering wheel. By causing the air bag to instantaneously inflate with explosively expanding working gas upon collision of a vehicle, an occupant's body which is inertially moving is supported with a reduced deceleration on the occupant's body so that the occupant can be protected from an impact of the collision.
There is also a trigger device for a gas generator which produces working gas to actuate these webbing pretensioner and air bag system in the event of a vehicular collision. Examples of such a trigger device include a mechanical trigger device making use of an inertia body which is displaced by a sudden deceleration occurred upon collision of a vehicle.
This trigger device has the structure that utilizes motion of the inertia body which is displaced by a collision. A firing pin which is normally held in an inoperative position is driven out toward a detonator, whereby the detonator is fired to ignite a propelling charge. The propelling charge is hence caused to burn, thereby obtaining explosively expanding actuating gas.
In a webbing pretensioner or air bag system equipped with a gas generator having such a mechanical trigger device, it is necessary to avoid any accidental actuation of such a webbing pretensioner or air bag system prior to its assembly on a vehicle and after assembly on the vehicle, to ensure its fail-free actuation in the event of an emergency such as a collision.
As will be described below, a variety of safety devices have therefore been proposed for mechanical trigger devices of gas generators so that the mechanical trigger devices are prevented from accidental actuation before their assembly in vehicles but are ensured to actuate subsequent to their assembly in the vehicles.
For example, Japanese Patent Application Laid-Open (Kokai) No. HEI 2-182555 laid open on Jul. 17, 1990 discloses a collision detecting device for a vehicle, which detects action of a deceleration of at least a predetermined value on the vehicle to actuate a webbing pretensioner so that upon collision of the vehicle, a webbing is tensioned to increase restraining force for an occupant. The collision detecting device is provided with setting means having a turnable member for selectively bringing the collision detecting device into an operative state or an inoperative state depending on the turned position and also with braking means having a pressing member arranged in opposition to a surface of the webbing. The turnable member and the pressing member are interlocked with each other by cam means, and the pressing member is pressed against or separated from the webbing depending on the turning of the turnable member.
According to this collision detecting device for the vehicle, the pressing member which is interlocked with the turnable member applies a brake to the webbing when the collision detecting device is selectively set in the inoperative state. The webbing therefore remains unusable insofar as the collision detecting device is not set in the operative state. This makes it possible to confirm the non-released state of the safety mechanism.
Further, U.S. Pat. No. 5,129,680 issued Jul. 14, 1992 to Shinji Mori discloses a pretensioner sensor suited for use with a webbing retractor for winding an occupant-restraining webbing in layers on a take-up shaft and adapted to actuate a pretensioner so that upon sudden deceleration of a vehicle, the webbing can be applied tightly onto an occupant. The pretensioner sensor is provided with release means for selectively bringing the pretensioner sensor into an operation-prevented state or an operative state, means for biasing the releasing means in the direction that the pretensioner sensor is maintained in the operation-prevented state, and means for fastening the webbing retractor and a vehicle body together. The fastening means has a fastening path at a position where the fastening means interferes with the fastening means. By moving a predetermined distance on the fastening path, the fastening means interferes with the releasing means against biasing force of the biasing means so that the release means brings the pretentioner sensor into the operative state. As long as the fastening means does not interfere with the release means, the pretensioner sensor is maintained in the operation-prevented state by the biasing force of the biasing means.
Upon mounting the webbing retractor on the vehicle body, for example, by using a bolt, a lever as the releasing means is turned against the biasing force of the biasing means by a free end of the bolt so that the pretensioner sensor can be brought into the operative state.
In addition, U.S. Pat. No. 5,149,134 issued Sep. 22, 1992 to Artur Fohl discloses a safety mechanism for a pretensioner of a vehicle seatbelt system in which a webbing retractor and a pretensioner trigger device are integrally assembled as a seatbelt assembly having a mounting flange and an inertia member is displaceably arranged in a housing to sense a deceleration of a vehicle. This safety mechanism is equipped with a displaceable, blocking member, a control member and a two-arm lever. The displaceable, blocking member makes the pretensioner inoperative and until the seatbelt assembly is mounted on a vehicle body, is maintained in engagement with the inertia member to block displacement of the inertia member. The control member extends from an inner side to an outer side of the housing and is displaceably attached to a wall of the housing. The control member is movable between a first position where the blocking member engages the inertia member and a second position where said blocking member is disengaged from the inertia member. The two-arm lever is pivotally mounted on the housing for moving the control member, and has a first arm with a sensing lug on its free end adjacent the mounting flange and a second arm engaging the control member.
Owing to the construction described above, mounting of the seatbelt assembly on the vehicle body results in holding of the first arm of the lever between the seatbelt assembly and the vehicle body. The lever is then allowed to pivot about a bearing pin so that the second arm causes the control member to move to the second position where the blocking member is disengaged from the inertia member. As a consequence, the inertia member is rendered displaceable, thereby making the pretensioner operative.
The collision detecting device disclosed in Japanese Patent Application Laid-Open (Kokai) No. HEI 2-182555 has the turnable member for selectively bringing the collision detecting device into the operative state or the inoperative state, the pressing member for pressing the webbing and the cam means for interlocking the collision detecting device and the pressing member, and has an extremely complex structure. The collision detecting device according to Japanese Patent Application Laid-Open (Kokai) No. HEI 2-182555 therefore involves the problem that it requires a high manufacturing cost.
The pretensioner sensor disclosed in U.S. Pat. No. 5,129,680 is accompanied by the problem that the lever as the releasing means may not turn and the pretensioner sensor may hence remain in the operation-prevented state if upon mounting the webbing retractor on the vehicle body by a bolt, tightening of the bolt is not sufficient or a worker erroneously uses a shorter bolt.
In this pretensioner sensor, the lever as the releasing means is turned using the bolt by which the webbing retractor is fastened to the vehicle body, so that the lever is located at a position hidden behind the vehicle body. There is accordingly the problem that the worker cannot directly check by his eyes if the lever has been turned correctly.
The safety mechanism for the pretensioner of the vehicle seat belt system, which is disclosed in U.S. Pat. No. 5,149,134, requires additional parts such as the lever so that a higher manufacturing cost is needed. Moreover, there is the potential danger that the control member may not move correctly and the pretensioner may not be brought into the operative state if upon mounting the webbing retractor on the vehicle body, the worker hits the vehicle body with the webbing retractor or accidentally drops the webbing retractor onto the floor and the lever is hence deformed. Since the webbing retractor is fastened to the vehicle body by bolts with the lever interposed therebetween, there is the potential danger that the webbing retractor may become inoperative because tightening of the fastening bolts may be insufficient or the fastening bolts may gradually become looser if the flatness of the lever is not sufficient or its coating film is too thick.